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16_4_Using_PSBTs_in_Libwally.md
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@ -4,11 +4,11 @@
You learned all about Partially Signed Bitcoin Transactions (PSBTs) in [§7.1](07_1_Creating_a_Partially_Signed_Bitcoin_Transaction.md) and [§7.2](07_2_Using_a_Partially_Signed_Bitcoin_Transaction.md), and as you saw in [§7.3: Integrating with Hardware Wallets](https://github.com/BlockchainCommons/Learning-Bitcoin-from-the-Command-Line/blob/master/07_3_Integrating_with_Hardware_Wallets.md), one of their prime advantages is being able to integrate with offline nodes, such as Hardware Wallets. HWI allowed you to pass commands to a Hardware Wallet, but what does the wallet itself use to manage the PSBTs? As it happens, it can use something like Libwally, as this section demonstrates. You learned all about Partially Signed Bitcoin Transactions (PSBTs) in [§7.1](07_1_Creating_a_Partially_Signed_Bitcoin_Transaction.md) and [§7.2](07_2_Using_a_Partially_Signed_Bitcoin_Transaction.md), and as you saw in [§7.3: Integrating with Hardware Wallets](https://github.com/BlockchainCommons/Learning-Bitcoin-from-the-Command-Line/blob/master/07_3_Integrating_with_Hardware_Wallets.md), one of their prime advantages is being able to integrate with offline nodes, such as Hardware Wallets. HWI allowed you to pass commands to a Hardware Wallet, but what does the wallet itself use to manage the PSBTs? As it happens, it can use something like Libwally, as this section demonstrates.
Basically, Libwally has all the PSBT functionality, so if there's something you could do with `bitcoind`, you could also do it using Libwally, even if your device is offline. What follows is the barest introduction to what's a very complex topic. Basically, Libwally has all of the PSBT functionality, so if there's something you could do with `bitcoind`, you could also do it using Libwally, even if your device is offline. What follows is the barest introduction to what's a very complex topic.
## Converting a PSBT ## Converting a PSBT
Converting a PSBT into Libwally's internal structure is incredibly easy, you just run `wally_psbt_from_base64` with a base64 PSBT (which means the outputs you received from `bitcoind`, like: Converting a PSBT into Libwally's internal structure is incredibly easy, you just run `wally_psbt_from_base64` with a base64 PSBT — which are the outputs produced by `bitcoin-cli`, such as:
`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` `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`
@ -112,7 +112,7 @@ Here's a similar example for the outputs:
``` ```
Obviously, there's a lot more you could look at in the PSBTs. In fact, looking is the main point of a PSBT: you can verify inputs and outputs from an offline computer. Obviously, there's a lot more you could look at in the PSBTs. In fact, looking is the main point of a PSBT: you can verify inputs and outputs from an offline computer.
> :warning: **WARNING:** These reading functions are _very_ rudimentary and will not work properly for extremly normal situations like an input or output that's still empty or that includes a `non_witness_utxo`. They will segfault if they aren't delivered a perfectly expected PSBT. A real reader would need to be considerably more robust, to cover all possible situations, and that's left as an exercise for the reader. > :warning: **WARNING:** These reading functions are _very_ rudimentary and will not work properly for extremly normal situations like an input or output that's still empty or that includes a `non_witness_utxo`. They will segfault if they aren't delivered a precisely expected PSBT. A real reader would need to be considerably more robust, to cover all possible situations, but that's left as an exercise for the reader.
### Testing Your PSBT Reader ### Testing Your PSBT Reader
@ -122,7 +122,7 @@ You can compile it as normal:
``` ```
$ cc examinepsbt.c -lwallycore -o examinepsbt $ cc examinepsbt.c -lwallycore -o examinepsbt
``` ```
The following PSBT from [§7.3](07_3_Integrating_with_Hardware_Wallets.md) can be used for testing as it matches the very narrow criteria required by this limited implementation: The following PSBT from [§7.3](07_3_Integrating_with_Hardware_Wallets.md) can be used for testing, as it matches the very narrow criteria required by this limited implementation:
``` ```
psbt=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 psbt=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
``` ```
@ -268,7 +268,7 @@ So, it's all there for your gathering!
## Creating a PSBT ## Creating a PSBT
As noted at the head of this section, all of the functions to need to create and process PSBTs are available in Libwally. Actually running through the process of doing so is complex enough that it's beyond the scope of this section, but here's a quick run-down of the functions required. Note that the [documents](https://wally.readthedocs.io/en/latest/psbt/) are out of date for PSBTs, so you'll need to consult `/usr/include/wally_psbt.h` for full information. As noted at the head of this section, all of the functions needed to create and process PSBTs are available in Libwally. Actually running through the process of doing so is complex enough that it's beyond the scope of this section, but here's a quick run-down of the functions required. Note that the [documents](https://wally.readthedocs.io/en/latest/psbt/) are out of date for PSBTs, so you'll need to consult `/usr/include/wally_psbt.h` for full information.
As discussed in [§7.1](07_1_Creating_a_Partially_Signed_Bitcoin_Transaction.md) there are several roles involved in creating PSBTs As discussed in [§7.1](07_1_Creating_a_Partially_Signed_Bitcoin_Transaction.md) there are several roles involved in creating PSBTs
@ -276,18 +276,19 @@ As discussed in [§7.1](07_1_Creating_a_Partially_Signed_Bitcoin_Transaction.md)
The creator role is tasked with creating a PSBT with at least one input. The creator role is tasked with creating a PSBT with at least one input.
This is a simple use of `wally_tx_init_alloc`, telling it how many inputs and outputs you'll have: A PSBT is created with a simple use of `wally_psbt_init_alloc`, telling it how many inputs and outputs you will eventually add:
``` ```
struct wally_psbt *psbt; struct wally_psbt *psbt;
lw_response = wally_psbt_init_alloc(0,1,1,0,&psbt); lw_response = wally_psbt_init_alloc(0,1,1,0,&psbt);
``` ```
But what you have is not yet a legal PSBT, because of the lack of inputs. You can create those by creating a transaction and set it as the global transaction in the PSBT, which updates all the inputs and outputs: But what you have is not yet a legal PSBT, because of the lack of inputs. You can create those by creating a transaction and setting it as the global transaction in the PSBT, which updates all the inputs and outputs:
``` ```
struct wally_tx *gtx; struct wally_tx *gtx;
lw_response = wally_tx_init_alloc(0,0,1,1,&gtx); lw_response = wally_tx_init_alloc(0,0,1,1,&gtx);
lw_response = wally_psbt_set_global_tx(psbt,gtx); lw_response = wally_psbt_set_global_tx(psbt,gtx);
``` ```
### Testing Your PSBT Creation ### Testing Your PSBT Creation
At this point, you should have an empty, but working PSBT, which you can see by compiling and running [the program](src/16_4_createemptypsbt.c). At this point, you should have an empty, but working PSBT, which you can see by compiling and running [the program](src/16_4_createemptypsbt.c).
``` ```
$ cc createemptypsbt.c -lwallycore -o createemptypsbt $ cc createemptypsbt.c -lwallycore -o createemptypsbt
@ -368,7 +369,7 @@ Following is a rough listing of functions for every roles; more functions will b
This section could be an entire chapter, as working with PSBTs at a low level is very intensive work that requires much more intensive manipulating of inputs and outputs than was the case in [Chapter 7](07_0_Expanding_Bitcoin_Transactions_PSBTs.md). Instead this section shows the basics: how to extract information from a PSBT, and how to begin creating one. This section could be an entire chapter, as working with PSBTs at a low level is very intensive work that requires much more intensive manipulating of inputs and outputs than was the case in [Chapter 7](07_0_Expanding_Bitcoin_Transactions_PSBTs.md). Instead this section shows the basics: how to extract information from a PSBT, and how to begin creating one.
> :fire: ***What is the Power of PSBTs in Libwally?*** Obviously, you can already do all of this in `bitcoin-cli`, and it's simpler because a lot of the drudgery is taken care of. The advantage of using Libwally is that it can be run offline, so it could be Libwally that's sitting on the other side of a hardware device that your `bitcoin-cli` is communicating to with HWI. This is, in fact, one of the major points of PSBTs: to be able to manipulate partially signed transactions without needing a full node. Libwally enables it. > :fire: ***What is the Power of PSBTs in Libwally?*** Obviously, you can already do all of this in `bitcoin-cli`, and it's simpler because Bitcoin Core manages a lot of the drudgery. The advantage of using Libwally is that it can be run offline, so it could be Libwally that's sitting on the other side of a hardware device that your `bitcoin-cli` is communicating to with HWI. This is, in fact, one of the major points of PSBTs: to be able to manipulate partially signed transactions without needing a full node. Libwally enables it.
## What's Next? ## What's Next?